1. Field of Invention:
This invention pertains to an artificial heart device for implantation within the chest cavity of a living being. More particularly, it relates to a total artificial heart which includes a semi-rigid shell construction having an internal compartment divided into a blood chamber and a pumping chamber which are separated by a flexible diaphragm.
2. Prior Art:
The successful long term operation of a total artificial heart embodying a blood chamber and a pumping chamber depends on the survivability of the intermediate flexible diaphragm. Over its expected lifetime, the flexible diaphragm will extend and collapse many millions cf times to provide the desired pumping action for blood through the total artificial heart. Many factors contribute to mechanical failure of the flexible diaphragm, usually characterized by splitting or other loss of structural integrity. Obviously, the failure of the flexible diaphragm results in failure of the pumping system, which may be fatal to a dependent patient.
A prior application filed under the title of "Elliptical Artificial Heart" discloses the use of multiple diaphragms including a blood diaphragm whose interior surface defines part of the blood containing compartment, and one or more pumping diaphragms which operate to collapse and extend the blood diaphragm to activate pumping action. These pumping diaphragms may be activated by pneumatic negative/positive pressure, or may be effected by a hydraulic fluid flow system operable under similar principles.
One of the major directions of research to control diaphragm survivability has been to develop predictable compositions with minimal elastic memory such that the folding patterns within the diaphragm become random. Failure to develop a random folding pattern results in a localized fold, which upon repeated folding movement, can weaken the localized diaphragm area. Accordingly, diaphragm compositions have included polyurethanes, Cardiothane.TM., Lycra.TM. and other materials whose elastic character enhances random folding patterns rather than repeated folding at the same location.
It has been discovered that even the best of compositions will ultimately succumb to material failure if localized folding of the diaphragm occurs a sufficient number of times. Ultimately, the molecular structure becomes weak following repeated similar folding at the same location. Once the molecular structure weakens, the diaphragm will favor folding at the weaker position, thereby aggravating the tendency of the diaphragm to continually fold at one location.
Particular locations of the diaphragm are very susceptible to recurring folding patterns, leading to diaphragm failure. One specific area of vulnerability is the peripheral edge of the diaphragm. A second area of common folding problem occurs because of the suction applied upon negative pressure through the pumping chamber. In prior art devices, pressure gradients within the pumping chamber would tend to favor specific diaphragm fold locations. Typically, these pressure gradients were most intense near the inlet opening for the pumping fluid. In very early embodiments, the diaphragm itself would be sucked into the inlet, creating abnormally high stress at that portion of the diaphragm.
What is needed is a diaphragm system which is better adapted to generate random folding patterns, and patterns which are not likely to create mechanical failure within the diaphragm structure. Not only is the primary diaphragm surface area of concern, but also the periphery structure where the diaphragm is attached to the interior housing of the total artificial heart compartment.